When I was a kid I read this joke:
"Is this yours? The name's all smudged."
"No, my name is Allsop."
I didn't quite understand it. I assumed the joke must be that the name "Allsop" apparently looked like a smudge of ink, and that Mr Allsop was saying "No, it's not smudged, my name really does look like that."
I also read a similar joke.
"Is this yours? The name's obliterated."
"No, my name's O'Brien."
I am ashamed to say that not only did I not notice the similarity between the two jokes, but I didn't know what "obliterated" meant either. (I'm not sure how old I was at this point) I thought it might mean "has an O' at the beginning" and the joke was that the foolish Mr O'Brien didn't realise his name was indeed "obliterated".
It was may years later, and, actually, many years after learning what "obliterated" really meant, that I noticed the similarity of the two jokes (some things just come to memory like that) - they were really just versions of the same joke: Person 1 is expressing that he can't read the name, Person 2 thinks that Person 1 *is* reading out a name similar to Person 2's real name.
Of the two, I think that the "O'Brien" version works better, as it's more plausible that someone might think "O'bliterated" is a real name than that they might think "Allsmudged" is. The only problem is that it's potentially insulting to Irish people, as it seems to belong on the same genre as the "Englishman, Irishman and Scotsman" or the "Pat and Mike" jokes, where a character's Irishness is used as a signpost that he is meant to be stupid.
The thing is, I don't think the joke is offensive unless you're already aware of the "Irish = stupid" tradition in so many other jokes. The guy isn't called "O'Brien" because it's a name befitting a stupid character, he's called "O'Brien" because it sounds vaguely like "obliterated". But unfortunately, because of all those *other* jokes, we have to put up with the "Allsmudged" version or risk offending someone. If it weren't for those jokes we could tell the "O'Brien" one to anyone we wanted and have a good old laugh together.